Gorenie i vzryv

The article considers results of a study on determining optimal areas for laser ignition of an oxygen–hydrogen fuel mixture in a model combustion chamber by focusing laser radiation to initiate an optical breakdown spark in a selected zone. The results of numerical simulation of the nonstationary process of mixing the gaseous components — oxygen and hydrogen — are presented with the determination of the parameters of the resulting mixture in the volume of the model combustion chamber carried out in the LOGOS-Prepost software package. Three zones that are most preferable for laser ignition in the chamber are selected among the zones in which focusing of radiation is possible during laser ignition. These zones are located in the regions of flow recirculation exhibiting fuel mixture compositions close to stoichiometric and low flow velocities. Preferential use of the zones for laser ignition selected by the results of the numerical simulation was confirmed by test fires.

The results of the third stage of numerical simulation of the ONERA LAPCAT II experiment on high-speed hydrogen combustion in a model duct are described. At this stage, the calculations are carried out taking into account the duct wall roughness and the presence of glass on the side walls. A synthetic turbulence generator is also added at the duct entrance and the initial field is obtained in a preliminary RANS (Reynolds-averaged Navier–Stokes) simulation using the nonlinear shear stress transport (SST-NL) model causing the emergence of secondary flows in channel corners. The simulation results obtained using the SST-based improved delayed detached eddy simulation (SST-IDDES) approach are presented. It is shown that the account for glasses affects the structure of separation regions but has little effect on average flow parameters and pressure distribution along the duct. The nonlinear model and the synthetic turbulence generation have a significant impact on all flow parameters.

Parameters of the jet of fire-extinguishing aerosol emanating from a high-pressure generator have been studied. The calculation of the exhaust nozzle of the generator using a fast-burning aerosol-forming composition has been performed. The characteristics of the formed supersonic flow with condensation of aerosol particles in it have been calculated and experimentally determined. It is shown that the aerosol jet formed by the high-pressure generator is capable of rising to three times the height than that attained using a device with a slow-burning aerosol-forming composition. This is due to the fundamentally different dynamics of the formed flow and the smaller size of aerosol particles condensing downstream the generator nozzle. Full-scale experiments have shown that the supply of fire-extinguishing aerosol to a height of about 9 m in conjunction with the flow of burning oil or gas provides an extremely short extinguishing time of the fountain of 3–5 s from the moment the generators start working. Extinguishing is achieved when filling the volume of the torch with a fire-extinguishing aerosol and reaching its minimum extinguishing concentration.

The article presents the results of multidimensional numerical calculations of direct detonation initiation and deflagration-to-detonation transition (DDT) in horizontal flat channels of different height filled with gaseous oxygen under normal conditions and with films of -heptane and -decane applied to the lower wall. The determining role of liquid fuel volatility in the mechanism of film detonation propagation is shown. The mechanism of detonation propagation in the system with an -heptane film is self-ignition of fuel vapors in the gas phase and in the system with an -decane film, it is the mechanical destruction of the film, evaporation of the resulting microdroplets, and self-ignition of fuel vapors in the gas phase. It is shown that during DDT in channels of different height with an -heptane film, preflame secondary explosions leading to DDT occur in a shock-compressed mixture of oxygen with preevaporated fuel near the leading shock wave (SW) but at a large distance from the film — in areas with elevated temperature and increased gas residence time. The SW velocity at the time of DDT is 800–900 m/s and the resulting detonation wave (DW) propagates at a speed exceeding 1300 m/s. At low ignition energies, there may be two limiting values of the channel height — minimum and maximum — at which DDT is still possible. The minimum channel height is determined by momentum and energy losses on the walls and the maximum is determined by the presence of an additional mechanism for evening the pressure in the flame.

A literature review on methods of activation of combustion of metallic fuels (MF) — Al and B — and their compounds in the composite propellant combustion is presented. The main ways and techniques aimed at increasing the completeness of MF combustion and the realization of its calorific value are considered, namely: the use of combined fuels, alloys, and mechanical activation; applying functional coatings to the surface of MF particles; making the composite conglomerates (granules); increasing the dispersion of MF; and the use of unconventional oxidizers and optimal binders. Some methods and ideas have been tested experimentally using a laboratory approach designed to compare a variety of MF. As a result, it seems promising to use mechanically activated aluminum diboride and activating additives in the propellant formulations and to increase the boron mass fraction in propellant over 40% provided that particles are protected from interaction with other propellant ingredients and the agglomeration is minimized.

Metal-free solid fuel compositions that do not have condensed combustion products are characterized by combustion instability. Refractory metal compounds are used as combustion stabilizers. It reduces the specific impulse and leads to the appearance of condensed combustion products. Allotropic modifications of carbon are flammable and can burn to gaseous products. In this work, the effect of detonation nanodiamond on the combustion of model solid fuel compositions containing a nitroether combustible binder with oxidizing agents and energetic fillers of various chemical structures has been investigated. The relationship between the effectiveness of the influence of detonation nanodiamond on the ballistic characteristics of solid fuel compositions and the chemical structure of the components included in their composition is shown.

The possibilities of increasing the shock wave energy of an underwater explosion by introducing the explosive with a positive oxygen balance into the composition of the energetic material are analyzed. For the calculations, relatively new compounds were chosen as explosive oxidizers: 3,6-dinitro-1,4-bis(trinitromethyl)-1,4-dihydropyrazolo[4,3-c]pyrazole; 4,4,5,5-tetranitro-2,2-bis(trinitromethyl)-2Н,2Н-3,3-bipyrazole; and2-dinitromethyl-5-nitrotetrazole. The function of explosive fuel was performed by the well-known powerful substances HMX and CL-20. The calculations have shown that compositions containing these explosive oxidizers should have high values of the TNT equivalent in terms of shock wave energy and the most noticeable increase in the TNT equivalent due to the use of these explosive oxidizers should be expected in the case of aluminized compositions.